New law requires ticket brokers to tell buyers if their ticket is with a major or regional carrier.
Enraged by safety errors in a deadly 2009 plane crash from Newark, New Jersey to Buffalo, New York, victims' family members marched to Washington and demanded change.
They got it in the form of a new law requiring airlines and travel websites to disclose who is flying each plane.
The flight that crashed en route to Buffalo, killing everyone onboard, was piloted by a small operator known as Colgan Air even though the plane said "Continental Connection" and travelers could book tickets directly through Continental.
Federal investigators found the distinctions can matter because of different levels of experience at the major carriers compared to regional airlines.
For example, Colgan's crew had far fewer hours in the cockpit than a flight team at Continental would require.
Experts theorized that might have made a difference as Flight 3407 made its icy approach to Buffalo Niagara International Airport when the pilot overreacted to a stall.
Now four weeks after the new law took effect, not everyone is following it.
For example: a search on Kayak.com still shows Newark-to-Buffalo flights on Continental.
Not until a user clicks through does it reveal the smaller carrier operates the flight.
Compare that to Travelocity, which displays the regional results on an initial search, as required by law.
Kayak declined several requests for comment from NBC News.
"They're not doing it, and we're going to find out why," said Senator Chuck Schumer, who had promised families in the Buffalo disaster there wouldn't be guesswork in the future.
Kayak could face a $25,000 fine for not complying with the legislation, which requires full disclosure of the operating airline in "the initial search."
Travelers admitted the whole thing can be confusing.
Nina Jordan took her boys to LaGuardia to watch their dad take off, but having booked online, she didn't know whether he was flying a major airline or a small carrier.
"They didn't specify," said the Port Jefferson mom. "You know, we bought the tickets online, and I'm assuming the big Airbus or big plane, but they didn't specify."
Tiki Lyons, who recently flew into New York from St. Louis, said she tells her travel agent to look for major carriers.
"People perceive the larger airlines as safer," she said.
Schumer's office said it would look into whether other travel websites are following the new disclosure law.
In the meantime, many passengers shrugged off the online confusion, saying they'd book a flight if it got them where they were going for the best price.
"If it goes where I want at the right time that's fine," said frequent flier Ted Levinson.